Low Magnetic Flux Research Articles

Characteristics of Fe-Si-B-P-Cu Nanocrystalline Soft Magnetic Alloy Powders With High Bs

Nanocrystalline soft magnetic alloy powders produced by heat treating amorphous powders are expected to improve properties and miniaturize dust cores because of their low coercive force Hc and high saturation magnetic flux density Bs. By water atomization process, we successfully obtained quenched Fe-Si-B-P-Cu alloy powders with spherical particle shape. The obtained powders have different average particle sizes of 2.0, 3.0, 5.0, and 8.5 μm. After annealing at 723 K, the as-quenched alloy powders are crystallized and Bs of the nanocrystalline alloy powders with Fe83.3Si4B8P4Cu0.7 and Fe84.8Si2B10P2Cu1.2 exhibit high Bs of 1.72 and 1.76 T, respectively. Core loss characteristics of the dust cores are found to be dependent on amorphous stability of the as-quenched powders. Thus, the Fe83.3Si4B8P4Cu0.7 nanocrystalline alloy powder with an average particle size of 3.0 μm exhibits the best core loss of 1461 kW/m3 (Bm = 50 mT, f=300 kHz).

Extremely Low Frequency Magnetic Flux Densities Measured Near Hospital in Tehran

The ever increasing rate of power consumption has led to an increase in public exposure to extremely low frequency magnetic fields (ELF-MFs) and brought severe concerns about their health effects. Considering previous studies and the facts about potential health effects of these fields, the present study aimed to evaluate the ELF-MF flux densities from power distribution lines near hospitals in Tehran. ELF-MF measurements were performed according to IEEE standard procedures-Std 644-1994 near the hospitals entrances using HI-3604 Power Frequency Field Strength Measurement System during three different time periods (i.e. 12-3 AM, 9-12 AM, 6-9 PM). The results were analyzed using One-Way ANOVA Test. Mean, minimum, and maximum values of ELF-MF flux densities were 0.165 ± 0.08 μT, 0.018 μT, 0.52 μT, respectively. There were no statistically significant differences in ELF-MF flux densities neither among different hospital groups nor among different time periods. The ELF-MF flux densities from power distribution lines around Tehran hospitals were much less than the standards values, implying that it can be considered only in epidemiological studies. In fact, in the case of powerful sources, magnetic field intensity is declined rapidly by distance and is limited to a few meters around the sources. This subject is considered as one of the main reasons for contradictory results in previous studies. Results of the present study can be used as a part of hospital patients’ exposure to quantify the total exposure levels of patients as a critical and sensitive group in Tehran hospitals.

Advection and dispersal of small magnetic elements in the very quiet Sun

We track small magnetic structures on very quiet regions (internetwork) of the Sun. We follow the footpoints of small-scale magnetic loops that appear on the photosphere at granular scales using spectropolarimetric and magnetographic data obtained with Hinode. We find two different regimes for their wanderings. Within granules (where they appear), they seem to be passively advected by the plasma – which is justified by their relatively low magnetic flux (~1016 Mx), and magnetic field strength (~200 G). The plasma flow thus traced is roughly laminar with a characteristic mean velocity of 2 km s-1 and very low vorticity. Once the magnetic markers reach intergranular lanes, they remain there and are buffeted by the random flows of neighbouring granules and turbulent intergranules, follow random walks, and disperse across the solar surface with a diffusion constant of 195 km2 s-1. While on their intergranular random walking, they may fall close to whirlpools (on scales ≲400 km) associated with convective downdrafts, similar to the events recently reported in mesogranular and supergranular cell boundaries tracking magnetic bright points, which provides additional evidence that these events are ubiquitous on the solar surface.

Geodynamo models: Tools for understanding properties of Earth’s magnetic field

Self-consistent models of the dynamo process in the Earth’s core have reached a state where they can be used to understand specific morphological and temporal properties of the geomagnetic field. Even though several parameters in the models are far from Earth values, systematic parameter studies resulted in scaling laws that suggest that the dynamical regime in the models is not dissimilar to that in the core dynamo. In some dynamo models the magnetic field shows a close similarity with the structure of the geomagnetic field at the core–mantle boundary and the models are used to infer the underlying flow pattern inside the core. They support the concept of convection columns aligned with the rotation axis that concentrate magnetic flux into four strong lobes near ± 65 ° latitude, and of rising plumes at the poles that are associated with low magnetic flux and westward vortex motion in the polar cap regions. Predictions for the field strength inside Earth’s core from dynamo models and inferences from observations of short-term changes of the field and changes in Earth’s rotation seem to converge at values of a few milliTesla. Dynamo models support the idea that the inhomogeneous thermal structure of the lower mantle has a significant influence on the dynamo and leads to a breaking of the longitudinal symmetry in the long-term geomagnetic field. In a limited range of control parameters the models show dipole polarity reversals that agree in detail with what is known about geomagnetic reversals, although the precise reversal mechanism in the models remains an open question.

Low core losses and magnetic properties of Fe85-86Si1-2B8P4Cu1 nanocrystalline alloys with high B for power applications (invited)

Recently, the energy crisis and the continued growth in electrical power generation strongly demand minimization of wasteful energy dissipation. Magnetic core loss (W) is the main source of energy dissipation in motors and transformers. This requires the development of soft magnetic materials with low coercivity (Hc) and high magnetic flux density (B). Fe-rich Fe85-86Si1-2B8P4Cu1 (at. %) alloy ribbons made from industrial raw materials (containing some impurities) with 6 mm in width have a heteroamorphous structure containing a large number of extremely small Fe grains (less than 3 nm), resulting from the unique effects of P and Cu addition in proper amounts. Crystallization of these alloys by annealing shows a uniform precipitation of α-Fe, leading to a uniform nanocrystallized structure of α-Fe grains, 16–19 nm in size, accompanied by an intergranular amorphous layer about 1 nm in width. The wide ribbons exhibit high B of 1.82–1.85 T (at 800 A/m), almost comparable to commercial oriented Fe–3 mass% Si alloys. Excellent magnetic softness (low Hc of 2.6–5.8 A/m, high permeability of 2.4–2.7 × 104 at 1 kHz and small saturation magnetostriction of 2.3–2.4 × 10−6) along with high electrical resistivity (0.67–0.74 μΩ m) of these alloys result in superior frequency characteristics of core losses and a much lower W at 50 Hz up to the maximum induction of 1.75 T, in comparison to the silicon steels now in practical use for power applications.

Empirical Modeling of Radiative versus Magnetic Flux for the Sun-as-a-Star

We study the relationship between full-disk solar radiative flux at different wavelengths and average solar photospheric magnetic-flux density, using daily measurements from the Kitt Peak magnetograph and other instruments extending over one or more solar cycles. We use two different statistical methods to determine the underlying nature of these flux-flux relationships. First, we use statistical correlation and regression analysis and show that the relationships are not monotonic for total solar irradiance and for continuum radiation from the photosphere, but are approximately linear for chromospheric and coronal radiation. Second, we use signal theory to examine the flux-flux relationships for a temporal component. We find that a well-defined temporal component exists and accounts for some of the variance in the data. This temporal component arises because active regions with high magnetic field strength evolve, breaking up into small-scale magnetic elements with low field strength, and radiative and magnetic fluxes are sensitive to different active-region components. We generate empirical models that relate radiative flux to magnetic flux, allowing us to predict spectral-irradiance variations from observations of disk-averaged magnetic-flux density. In most cases, the model reconstructions can account for 85-90% of the variability of the radiative flux from the chromosphere and corona. Our results are important for understanding the relationship between magnetic and radiative measures of solar and stellar variability.

Impact of magnetic field gradients on the free corrosion of iron

Abstract The influence of magnetic fields oriented parallel and perpendicular to the electrode surface on the corrosion behaviour of differently shaped iron samples in low concentrated sulphuric acid solutions has been studied. It is demonstrated, that the relative sample-to-magnet configuration, which determines the magnetic flux density distribution in front of the electrode surface, is decisive for the free corrosion activity. In a configuration generating low magnetic flux density gradients the Lorentz force driven micro-convection leads to an anodic shift of the free corrosion potential. In contrast, a configuration yielding high magnetic flux density gradients causes a cathodic potential shift and leads to a suppression of the corrosion reaction. These effects are discussed on the basis of the Lorentz force and the magnetic field gradient force acting on the partial reaction steps during the corrosion process.

Auditory Cortex Signal Detected by Potassium Alkali Vapour Magnetometer

Event Abstract Back to Event Auditory Cortex Signal Detected by Potassium Alkali Vapour Magnetometer Kiwoong Kim1*, Samo Begus2 and Mike Romalis3 1 Korea Research Institute of Standards and Science, South Korea 2 Faculty of Electrical Engineering, Slovenia 3 Princeton University, United States In this work we shall present the detection of brain magnetic field caused by stimulated auditory cortex and detected by a noncryogenic atomic magnetometer. In comparison with the superconducting quantum interference device (SQUID) magnetometers, which so far have been used to measure magnetic field of the brain, atomic magnetometers have advantages of comparable or higher sensitivity, no need for cryogenics and easy to implement multi-channel recording. The magnetometer is based on the measurement of electron Larmor spin precession in a vapour of potassium atoms. It operates in spin-exchange relaxation-free (SERF) regime at low magnetic flux densities and high alkali-metal vapour density [1]. The potassium cell is placed inside magnetic shield which is permanently opened on one side for subject access. The polarization rotation of the probe beam is measured using a polarization modulation technique. Magnetometer signals were recorded with the two dimensional photodetector array and data acquisition system performing lock-in demodulation using field programmable gate array [2]. The direction of the pump beam could be changed during the measurement to enable magnetometer measurement of brain signal in two directions. Audio stimulation has been performed by pneumatic earphone and short 1 kHz pulse trains. After rejecting the heart beat signals and disturbances due to mechanical vibrations the N100m could be seen.

Development of ELF Band Receiver of Detecting Extreme Low Frequency Magnetic Flux Variation Due to Earthquakes

ELF (30-300 Hz) band three-axial magnetic-flux receiver was developed for detecting electromagnetic-wave precursor of earthquakes and volcanic eruption. The receiver attained a high sensitivity of 0.4pT/√Hz (223Hz) and 4.5 pT/√Hz (17Hz) for the ground based observation of the ambient magnetic flux anomaly. The receiver was extended to detect ultra-low-frequency (ULF) variation (0.1 to 10-7Hz) of crust magnetic flux by through MMD (Modulated Magnetic-flux Detection) reception. It detects the modulated components of the ELF band atmospheric signal which are produced by the crust ULF magnetic-flux variation. The receiver noise due to the artificial noise can be smoothed out from the objective ULF magnetic flux signal by introducing long term integration for the period of 107 seconds of the detected signal. The receiver detected the ULF anomaly of magnetic variation and the Schumann Resonance variation appeared before the two earthquakes of the class M7 occurred in Japan in 2005 and 2007 respectively.

Effect analysis of magnetic annealing below Curie-temperature on the magnetic properties of electrodeposited nickel–iron

Electrodeposited nickel–iron is used as a functional layer in inductively working micromagnetometers. The magnetic properties of this layer, which builds up the flux guiding core structure of helical copper coils, have a crucial influence on the operation of the sensors. Low coercitive field strengths and high magnetic saturation flux densities of the ferromagnetic cores are required for excellent sensor characteristics. In this paper we present an innovative magnetic treatment below Curie-temperature of electrodeposited nickel–iron as well as an effect analysis of the MEMS fabrication process regarding the options of seed layers for electrodeposition.

Nonzero electron temperature effects in nonlinear mirror modes

The nonlinear theory of the magnetic mirror instability (MI) accounting for nonzero electron temperature effects is developed. Based on our previous low-frequency approach to the analysis of this instability and including nonzero electron temperature effects a set of equations describing nonlinear dynamics of mirror modes is derived. In the linear limit a Fourier transform of these equations recovers the linear MI growth rate in which the finite ion Larmor radius and nonzero electron temperature effects are taken into account. When the electron temperature Te becomes of the same order as the parallel ion temperature T∥ the growth rate of the MI is reduced by the presence of a parallel electric field. The latter arises because the electrons are dragged by nonresonant ions which are mirror accelerated from regions of high to low parallel magnetic flux. The nonzero electron temperature effect also substantially modifies the mirror mode nonlinear dynamics. When Te≃T∥, the transition from the linear to nonlinear regime occurred for wave amplitudes that are only half that which was inherent to the cold electron temperature limit. Further nonlinear dynamics developed with the explosive formation of magnetic holes, ending with a saturated state in the form of solitary structures or cnoidal waves. This shows that the incorporation of nonzero temperature results in a weak decrease in their spatial dimensions of the holes and increase in their depth.

Analysis of low-temperature-fired NiCuZn ferrites for power applications

NiCuZn ferrite materials fired at low temperature and containing 1.5 wt.% Bi 2O 3 and different Co 2O 3 concentrations have been prepared by the conventional ceramic technique. The samples were sintered for 4 h in air at 900 °C. The initial permeability decreased with the Co 2O 3 content due to local anisotropy induced by Co ions. The saturation magnetization increased with the Co 2O 3 content, which is attributed to the preference of Co ions for octahedral sites and their higher magnetic moment than those of Ni and Cu ions. Power loss under excitation at low magnetic flux density and low frequency first decreased, and then increased with increasing Co 2O 3 content due to the collective influence of the local induced anisotropy and the initial permeability. When the excitation frequency increased to 1 or 10 MHz, the power loss gradually decreased with increasing Co 2O 3 content, mainly because Co ions can decrease the concentration of Fe 2+ leading to a decrease in eddy current loss and residual loss for the ferrite samples. With increasing induction flux density, the effect of domain wall “freezing” caused by Co ions gradually disappears. For a flux density greater than or equal to the critical value of 50 mT, Co 2O 3 addition has a negative influence on decreasing the power loss of NiCuZn ferrites fired at low temperature.

Magnetic structure and magnetoresistance of patterned epitaxial iron thin films: The influence of shape and magnetocrystalline anisotropy

A magnetic-force-microscopy investigation is conducted into the influence of the shape and magnetic anisotropy on the magnetic structure and the mode of magnetization reorientation in epitaxial iron thin films patterned by subtractive techniques. Magnetic anisotropy is found to have a strong influence on the magnetic structure. With an applied field directed along a specimen, the latter is in a single-domain state when oriented parallel to the easy axis of magnetization, and is in a multidomain state when oriented perpendicular to the easy axis, the domain magnetic moments being parallel to the easy axis in both cases. The magnetic structure appears as a streaky pattern. Magnetization reorientation proceeds by domain-wall motion in both cases. The tanks do not change the mechanism of magnetization reorientation in the rectangular part, yet they ensure a single-domain state at lower magnetic flux densities. The results should offer some scope for using epitaxial iron thin films of suitable shape and crystallographic orientation in spin-valve injectors or detectors.

Properties of the electron beam in a room-temperature electron beam ion source investigated by position sensitive x-ray detection

The evolution of the charge state distribution inside an electron beam ion source or trap (EBIS/T) is determined by interactions of the electron beam with the ions in the trap region. Hence, detailed information about the electron beam is required for evaluations of spectroscopic and ion extraction measurements performed at EBIS/T facilities. This article presents the results of investigations on the electron beam properties of an ion source of the Dresden EBIS type. For the first time theoretical predictions of the shape of the beam were tested for a noncryogenic EBIS working with low magnetic flux densities provided by permanent magnets. Position and width of the electron beam were measured at different electron energies showing an oscillation in the beam structure. At an energy of E(e)=16 keV and an emission current of I(e)=30 mA the beam is compressed to a radius of r(e)=57 mum (80% current). This refers to an average current density of j(e)=232 A/cm(2).

Study on Homopolar Superconductivity Synchronous Motors for Ship Propulsion Applications

Superconductivity synchronous motors compared with conventional motors can reduce the motor size and enhance the motor efficiency for low-speed and high torque applications under the space constraints for propulsion system. Especially, homopolar superconductivity synchronous motors (HSSMs) need less superconductor and lower magnetic flux density in superconductor field coil than air-cored superconductivity synchronous motors (ASSMs). In addition, mechanical structure is more simplified and stability is increased because the superconductor field coil of HSSMs is not rotated in operation. In this paper, we present the outline of HSSMs including structure, characteristics and operational principles with the conceptual design of HSSM.

Self-Consistent Current Density Calculation for HTS Coils

The maximum current that a high-temperature superconducting (HTS) coil can achieve is typically calculated assuming uniform current density within the tape in the presence of a flux density gradient within the coil. This solution is not consistent with the current density and flux density, or , dependence of the HTS tapes and more current flows in areas of lower magnetic flux density. For some designs, this error is small, but it can be significant in other cases. This paper presents a method for computing the self-consistent critical current distribution within an HTS by imposing the condition that there is no voltage gradient across the width of an individual tape. The expected increase in critical current is predicted to be as high as 25% for some cases.

環境対応Ｐｂレス焼結電磁ステンレス材の開発

In recent years, melted electromagnetic stainless steels containing a small amount of lead (Pb) have been used in the majority of magnetic parts in which corrosion resistance is required, beginning with solenoid valves and also including injectors for fuel injection systems and various other types of actuators. In these fields, the development of various types of sintered magnetic cores using the powder metallurgy method has been attempted in the past. But because it was not, however, possible to solve problems such as low magnetic flux density and excessive core loss, etc., these products have not reached application. This is attributable to the low density at 7.0 Mg/m3 of the conventional sintered electromagnetic stainless steel, SUS410, which made it impossible to obtain high magnetic flux density and satisfactory suction. Therefore, the authors developed a new sintered electromagnetic stainless steel with greatly improved compactibility and sinterability by optimizing the powder composition and annealing treatment. The developed sintered electromagnetic stainless steel has an Fe-6.5Cr-3Si composition with no Pb, considering the environment. Satisfactory compactibility is maintained in spite of the high content of Si at 3 mass%, and a high density ratio of more than 95% (7.4 Mg/m3) can be obtained after sintering. As a result, the developed material realized a sintered electromagnetic stainless steel with both a high magnetic flux density of B2500A/m: 1.4 T and satisfactory permeability of μm: 5000, which are necessary in actuators, as well as airtightness, which is important as a functional property in injectors. The mass production of the injectors core for LPG engines began in September 2005.

Low frequency magnetic emissions and resulting induced voltages in a pacemaker by iPod portable music players

BackgroundRecently, malfunctioning of a cardiac pacemaker electromagnetic, caused by electromagnetic interference (EMI) by fields emitted by personal portable music players was highly publicized around the world. A clinical study of one patient was performed and two types of interference were observed when the clinicians placed a pacemaker programming head and an iPod were placed adjacent to the patient's implanted pacemaker. The authors concluded that "Warning labels may be needed to avoid close contact between pacemakers and iPods". We performed an in-vitro study to evaluate these claims of EMI and present our findings of no-effects" in this paper.MethodsWe performed in-vitro evaluations of the low frequency magnetic field emissions from various models of the Apple Inc. iPod music player. We measured magnetic field emissions with a 3-coil sensor (diameter of 3.5 cm) placed within 1 cm of the surface of the player. Highly localized fields were observed (only existing in a one square cm area). We also measured the voltages induced inside an 'instrumented-can' pacemaker with two standard unipolar leads. Each iPod was placed in the air, 2.7 cm above the pacemaker case. The pacemaker case and leads were placed in a saline filled torso simulator per pacemaker electromagnetic compatibility standard ANSI/AAMI PC69:2000. Voltages inside the can were measured.ResultsEmissions were strongest (≈ 0.2 μT pp) near a few localized points on the cases of the two iPods with hard drives. Emissions consisted of 100 kHz sinusoidal signal with lower frequency (20 msec wide) pulsed amplitude modulation. Voltages induced in the iPods were below the noise level of our instruments (0.5 mV pp in the 0 – 1 kHz band or 2 mV pp in the 0 – 5 MHz bandwidth.ConclusionOur measurements of the magnitude and the spatial distribution of low frequency magnetic flux density emissions by 4 different models of iPod portable music players. Levels of less than 0.2 μT exist very close (1 cm) from the case. The measured voltages induced inside an 'instrumented-can' pacemaker were below the noise level of our instruments. Based on the observations of our in-vitro study we conclude that no interference effects can occur in pacemakers exposed to the iPod devices we tested.

Spectropolarimetric Inversions of the Caii8498 and 8542 A Lines in the Quiet Sun

We study non-LTE inversions of the Ca II infrared triplet lines as a tool for inferring physical properties of the quiet Sun. The inversion code is successful in recovering the temperature, velocity, and longitudinal magnetic flux density in the photosphere and chromosphere, but the height range where the inversions are sensitive is limited, especially in the chromosphere. We present results of inverting spectropolarimetric observations of the lines in a quiet-Sun region. We find three distinct ranges in chromospheric temperature: low temperatures in the internetwork, high temperatures in the enhanced magnetic network, and intermediate temperatures associated with low magnetic flux regions in the network. The differences between these regions become more pronounced with height as the plasma-β decreases. These inversions support the picture of the chromosphere, especially close to the magnetic network, being highly inhomogeneous in both the vertical and horizontal directions.

ELF‐magnetic flux densities measured in a city environment in summer and winter

Epidemiological studies have indicated a connection between extremely low frequency magnetic flux densities above 0.4 microT (time weighted average) and childhood leukemia risks. This conclusion is based mainly on indoor exposure measurements. We therefore regarded it important to map outdoor magnetic flux densities in public areas in Trondheim, Norway. Because of seasonal power consumption variations, the fields were measured during both summer and winter. Magnetic flux density was mapped 1.0 m above the ground along 17 km of pavements in downtown Trondheim. The spectrum was measured at some spots and the magnetic flux density emanated mainly from the power frequency of 50 Hz. In summer less than 4% of the streets showed values exceeding 0.4 microT, increasing to 29% and 34% on cold and on snowy winter days, respectively. The average levels were 0.13 microT (summer), 0.85 microT (winter, cold), and 0.90 microT (winter, snow), with the highest recorded value of 37 microT. High spot measurements were usually encountered above underground transformer substations. In winter electric heating of pavements also gave rise to relatively high flux densities. There was no indication that the ICNIRP basic restriction was exceeded. It would be of interest to map the flux density situation in other cities and towns with a cold climate.